The present disclosure relates to a fixing unit configured to fix a toner image on a recording medium and an image forming apparatus including this.
An electro-photographic image forming apparatus includes a fixing unit configured to fix a toner image on a recording medium such as a sheet of paper.
The fixing unit includes a fixing roller pair heating and fixing the toner image on a sheet. A heat-resistant bushing is disposed between a shaft and a bearing of at least one roller of the fixing roller pair. The heat-resistant bushing is provided to block the heat from being transmitted from the shaft of the roller to the bearing. The heat-resistant bushing is fixed to the shaft of the roller by a retaining ring and rotates integrally with the shaft of the roller. Because the heat-resistant bushing and the roller shaft do not slip with each other, it is possible to prevent noise from being generated by friction.
Still further, the heat-resistant bushing is configured such that thermal expansion thereof is suppressed by setting a coefficient of thermal expansion thereof to be lower than that of the roller shaft. In general, the fixing roller pair (roller shaft) is formed of metal such as iron and stainless steel to be able to sustain high temperature. Meanwhile, the heat-resistant bushing is formed of a material that does not transmit the heat from the shaft of the roller to the bearing.
However, the fixing unit described above requires the retaining ring to fix the heat-resistant bushing to the roller shaft. Therefore, it is costly to manufacture the retaining ring and it takes time and cumbersome works to attach the retaining ring. Besides that, because the heat-resistant bushing of the fixing unit described above must be formed of a material whose coefficient of thermal expansion is lower than that of the metallic roller shaft and which is capable of shutting off the heat, a considerable restriction is imposed in selecting the material.